Question 1:
An important service provided by any system is the ability to run a process on a predetermined schedule without human intertention. The "automation" of tasks can reduce the workload of the system administrator significantly. Unfortunately Linux currently offers not one service but potentially three-cron, anacron, and systemd timer units.
In about a page compare and contrast all three systems. Illustrate your discussion by using the system files /etc/anacron and /etc/crontab and by constructing equivalent systemd service and timer files.
Notes:
a. It says "compare" and "contrast"-so explain how they are the same and how they are different.
b. Your answers must be written in your own words.
c. Please use the specified system files to explain how scheduling is defined do not invent your own.
d. Any technical term used must be explained.
e. Do not discuss the package systemd-cron. Write and test the systemd service and timer files yourself.
f. One way to test a crontab file or a anacrontab file, or sys- temd service and timer files is to use the date command as the command ultimately to be run the output from the command ef- fectively timestamps when it was run by your scheduler.
g. Some sources of information: Cron:
• The text book
• man 5 crontab
Anacron:
• The text book
• man 5 anacrontab
Systemd timer unit:
• https://wiki.archlinux.org/index.php/Systemd/ Timers
• https://www.certdepot.net/rhel7-use-systemd-timers/
h. List all resources used in answering the question.
Question 2:
The web administrator of your organisation needs to login remotely to the machine that is running the organisation's public web site.
You tell her that the only way to login is via The Secure Shell-which she knows nothing about! Assuming she is logging in via a Linux box write a help document for her containing the following-
a. A short introduction to SSH, explaining why it is the preferred way of logging into a remote machine-this explanation will need to discuss symmetric and asymmetric key encryption.
b. A discussion of the contents of the file
~/.ssh/known_hosts.
Your discussion should include (but not be limitted to):
• how the file is populated,
• how the keys in the file are used by SSH,
• a discussion of "man-in-the-middle" attacks,
• why the hostnames in the file are "hashed", and
• how individual keys can be deleted by ssh-keygen.
c. A description how to configure access so that no pass- words are needed-that is by using user asymmetric keys. This will require a discussion (with examples) of the command ssh- keygen, the file ~/.ssh/authorized_keys, passphrase pro- tected keys and the commands ssh-agent and ssh-add.
Notes:
a. Any technical term used must be explained.
b. Your virtual Debian has the SSH dæmon installed and running by default-so you can SSH to it from the host system or from a second virtual machine.
c. Your virtual machine has two network interfaces configured-a host only interface and a NAT interface. To bring the host only network "up" study the man pages interfaces(5), ifup(8) and ifdown(8).
d. You must show the relevant changes/parts of any files discussed.
e. This is a help document so you must explain (in your own words) the purpose of every file and command mentioned (plus any com- mand line options).
f. Be very clear which key (public or private) is stored on which machine (remote or local)
g. Port forwarding, SSH tunnels and firewalls need not be discussed- they will be covered later in the course.
Question 3:
a. In about a page explain in your own words what a Logical Volume Manager is, its purpose and why it is useful.
b. Illustrate your explanation by using the Linux Log- ical Volume Manager to combine the two spare disks available on the Virtual Debian distribution. Combine the two disks into one logical volume. Format the new logical disk and modify the /etc/fstab file to mount the new disk at boot.
c. Document and explain in your own words the purpose of every command you use (plus any command line options) and any configuration files or scripts you modify or create.
Notes:
a. Be certain to explain the meaning of any tehnical terms you may use-for example, what is a "physical volume", a "volume group", &c.
b. Make use of the utilities pvdisplay, vgdisplay, &c. to show the results of commands and that they have worked.
Question 4:
A user comes to you requesting that you create and implement a backup policy for his desktop machine. What he wants, is to be able to place a blank DVD in his Single-Sided DVD-burner at the end of the working day on a Friday and have all the files he has been working on for the week backed up automatically that evening to the DVD!
After a bit more questioning you find out that:
• He frequently creates/deletes and changes files on a daily basis.
• He wants to be able to recover files for any given day.
• He only wants his home directory backed up.
• His home directory contains about 2Gbytes of data.
• His desktop machine has a spare disk (mounted as /spare) that has plenty of free space for temporary storage.
Tasks that need to be done:
a. Using the information above design a backup policy. Give a detailed description and justification of your backup-policy.
b. Using tar, a shell script or scripts and systemd timer and service files to implement your backup policy.
Notes:
a. Explain in your own words each operation you needed to perform to implement your backup policy. Your descriptions of each oper- ation need to show you understand the purpose of the operation.
b. Use /spare as a temporary storage for backup files until they are burnt to the DVD on Friday.
c. "Temporary Storage" means just that-cleanup /spare after a successful burn.
d. A Single-sided DVD can only hold 4.2GiB (4.2×1024×1024×1024 bytes) of data.
e. The ISO9660 file-system-is the file-system used on Optical disks.
f. To write data to an optical disk a complete ISO9660 disk image file containing the data, must be created on the local hard disk and then burnt to the optical disk.
g. You will need utilities for creating ISO9660 images and burning DVDs, have a look at the following packages dvd+rw-tools, genisoimage, wodim.
h. List all resources used in answering the question.